This application relates generally to disc drive servo track writers, and more particularly to a servo track writer that is filled with a relatively low-density gas during the servo writing process.
A disc drive typically includes a base to which various components of the disc drive are mounted. A top cover cooperates with the base to form a housing that defines an internal, sealed environment for the disc drive. The components include a spindle motor, which rotates one or more discs at a constant high speed, and an actuator assembly for writing information to and reading information from circular tracks on the discs. The actuator assembly includes a plurality of actuator arms extending towards the discs, with one or more flexures extending from each of the actuator arms. Mounted at the distal end of each of the flexures is a read/write head, which includes an air bearing slider enabling the head to fly in close proximity above the corresponding surface of the associated disc during operation of the disc drive. When the disc drive is powered down, the heads may be moved to a landing zone at an innermost region of the discs where the air bearing sliders are allowed to land on the disc surface as the discs stop rotating. Alternatively, the actuator assembly may move (unload) the heads beyond the outer circumference of the discs so that the heads are supported away from the disc surface by a load/unload ramp when the drive is powered down.
Disc drives typically include a servo system for controlling the position of the heads during both seeking operations (moving from one track to another) and read/write operations where the head must precisely follow the circular track. One type of servo system is a dedicated servo system where one entire disc surface contains servo information written as dedicated tracks. The remaining disc surfaces within the drive are thus used to store data on dedicated data tracks. Another type of servo system, known as an embedded servo system, provides servo information on each of the disc surfaces embedded between data portions. Well known state estimator circuitry is used to estimate the position of the heads at such timesthat the heads are not located over the embedded servo information.
With both dedicated and embedded servo disc drives, servo information or patterns are typically recorded on the target disc by a servo-track writer assembly (xe2x80x9cSTWxe2x80x9d) during the manufacture of the disc drive. One conventional STW records servo patterns on the discs following assembly of the disc drive. In this embodiment, the STW attaches directly to a disc drive and uses the drive""s own read/write heads to record the requisite servo patterns to the mounted discs. An alternative method for servo pattern recording utilizes a separate STW apparatus having dedicated servo recording heads for recording the servo patterns onto one or more discs simultaneously prior to the assembly of such discs within a disc drive.
Regardless of whether the servo information is written to the discs prior to assembly within a disc drive (i.e., using a separate STW assembly having a dedicated actuator assembly) or following assembly of a disc stack within a disc drive (i.e., using the actuator assembly of the disc drive), it is crucial to provide a highly accurate positioning system with the STW to ensure accurate placement of the servo information on the discs. Specifically, a STW includes a positioning system for moving the actuator assembly and the attached heads across the disc surfaces during the servo writing procedure. The STW further includes a highly precise position detection system (often times incorporating a laser) for determining the position of the actuator assembly during the servo writing procedure. The position detection system provides correction signals to a motor within the positioning system to correct any errors in the position of the servo heads during operation of the STW.
In a continuing effort to store more data onto existing or smaller-sized discs, the capacity of each disc or platter is increased by increasing the track density (i.e., the number of tracks per inch). Increased track densities require more closely-spaced, narrow tracks and therefore enhanced accuracy in the recording of the servo patterns onto the target disc surface. However, as the track density increases, it becomes increasingly likely that errors will be encountered during the servo writing process. For example, the servo writing head may experience resonance vibrations during operation which alters the position of the head as the servo information is written. Such vibrations can lead to inaccurate servo information being written to the disc surface which, in turn, limits the ability of the disc drive to accurately position the data head over the desired data track during normal track following procedures (i.e., during normal read and write operations).
The resonance vibrations experienced by the head during the servo writing process are typically caused by the high-speed rotation of the discs within the STW. That is, regardless of whether the STW utilizes the disc drive itself or a separate, dedicated apparatus, the rotation of the discs within the STW (at speeds of up to 10,000 revolutions per minute or more) causes a great deal of air turbulence within the STW. This turbulence results from friction between the spinning disc surfaces and the air within the STW and represents a known phenomenon in the disc drive art. The air turbulence within a STW also impacts other components within the STW such as the actuator arms and the heads flying over the discs.
One proposed solution for reducing air turbulence while writing servo information to the discs within a previously assembled disc drive is to partially fill the drive with helium gas during the servo writing process, thereby reducing the overall density of the gas within the disc drive. Specifically, reducing the density of the gas within the STW acts to reduce the frictional forces applied to the spinning discs, thereby reducing the drag-induced vibrations on the discs and the actuator assembly. However, because disc drives are not hermetically sealed during the servo writing process, it is difficult to achieve a desired helium concentrations within the disc drive due to the tendency of the helium gas to escape the confines of the drive during operation of the STW.
Accordingly there is a need for an improved STW that can detect helium leaks and maintain relatively high concentrations of helium or other low-density gases within the STW for the duration of the servo writing process. Furthermore, there is a need for both a helium-filled STW that works with previously assembled disc drives as well as a helium-filled STW that has dedicated servo heads for writing servo information to discs prior to assembly of the discs within a disc drive. The present invention provides a solution to this and other problems, and offers other advantages.
Against this backdrop the present invention has been developed. In accordance with one embodiment of the present invention, a method detects leaks of a low-density gas from an enclosure containing a rotating storage disc, where the low-density gas reduces drag-induced vibrations generated by the rotating disc. The method includes monitoring a signal which varies in response to variations in the concentration of the low-density gas in the enclosure and adding additional quantities of the low-density gas to the enclosure when the monitored signal indicates that the concentration has dropped below a predetermined level.
Monitoring the concentration of the low-density gas may include monitoring actual concentration levels of the gas using a pressure sensor located within the enclosure, or may include directly monitoring disc mode vibration amplitudes using an accelerometer. Alternatively, a sensor may be used to indirectly measure the amplitudes of the drag-induced vibrations. Such a sensor may include a laser Doppler vibrometer, a capacitance probe, or the servo head position feedback circuitry found within a disc drive or a dedicated servo track writer.
Another embodiment of the present invention is a servo writing assembly that includes a STW having a base for supporting a spindle motor that rotates the disc and a servo writing head that writes servo patterns on the rotating disc. A cover attached to the base forms an enclosed interior environment within the STW and includes a sealable opening for loading the disc within the STW. The cover further includes an inflow port for directing the low-density gas into the interior environment of the STW prior to writing servo patterns on the disc. The assembly further includes a sensor for detecting when a concentration of the gas within the STW drops below a predetermined minimum level so that additional quantities of the gas can be added until the concentration again exceeds the predetermined minimum level. The sensor may be an accelerometer attached either to the spindle motor of a disc drive inserted within a STW or to a dedicated spindle motor of a MDW. Alternatively, the sensor may indirectly measure amplitudes of the vibrations generated by the rotating storage disc. Such a sensor may include a laser Doppler vibrometer, a capacitance probe or the servo head position feedback circuitry found either in a disc drive or in a dedicated servo track writer. The dedicated servo track writer may comprise a MDW having a plurality of servo writing heads and a dedicated spindle motor for supporting a plurality of discs.
The present invention can further be implemented as a servo writing assembly having an enclosure defining an interior volume filled with low-density gas and supporting a rotating storage disc. The servo writing assembly includes means for detecting when a concentration of the low-density gas within the enclosure has dropped below a predetermined minimum level. The detecting means may include means for indirectly detecting the magnitude of drag-induced vibrations that grow in intensity as the low-density gas leaks from the enclosure and is replaced by air.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.